An optical device is provided which includes a slab waveguide and at least one input waveguide coupled to a first side of the slab waveguide. The device also includes a plurality of output waveguides coupled to a second side of the slab waveguide. The slab waveguide has a segmented transition region that includes a plurality of waveguiding regions spaced apart from one other by at least one discrete sector.
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1. An optical device comprising:
a slab waveguide;
at least one input waveguide coupled to a first side of the slab waveguide;
a plurality of output waveguides coupled to a second side of the slab waveguide;
wherein said slab waveguide has a segmented transition region that includes a plurality of waveguiding regions being spaced apart from one other and isolated from one another by at least one discrete sector having a lower refractive index than said waveguiding regions.
12. A planar light-guide circuit, comprising:
a substrate;
a slab waveguide located on said substrate;
at least a first waveguide located on said substrate and coupled to a first side of the slab waveguide;
at least a plurality of second waveguides located on said substrate and coupled to a second side of the slab waveguide;
N waveguiding regions, where N is an integer greater than or equal to 2, said waveguiding regions being located within said slab waveguide and being spaced apart and isolated from one another by discrete segments having predetermined widths and a lower refractive index than said waveguiding regions.
19. An optical device, comprising
a first star coupler having a first waveguide array that is coupled to a first slab waveguide;
a second star coupler having a second waveguide array that is coupled to a second slab waveguide;
N waveguiding regions, where N is an integer greatcr than or equal to 2, said waveguiding regions being located within said second slab waveguide and being spaced apart and isolated from one another by discrete segments having predetermined widths and a lower refractive index than said waveguiding regions;
a grating comprising a plurality of waveguides having unequal optical path lengths, said grating interconnecting the first and second star couplers.
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The present invention relates generally to optical components employed in optical transmission systems, and more specifically to a technique for reducing the insertion loss of an optical component having an array of input and output waveguides.
WDM optical transmission systems employ a variety of different passive components. Such components are increasingly being fabricated on Planar Light-Guide Circuits (PLC). A planar lightguide circuit, also known as an optical integrated circuit, can be readily mass produced because the processing steps are compatible with those used in silicon integrated circuit (IC) technology, which are well known and geared for mass production.
One common type of planar lightguide circuit employs doped-silica waveguides fabricated with silicon optical bench technology. Doped-silica waveguides are usually preferred because they have a number of attractive properties including low cost, low loss, low birefringence, stability, and compatibility for coupling to fiber. Such a planar lightguide circuit is fabricated on a carrier substrate, which typically comprises silicon or silica. The substrate serves as a mechanical support for the otherwise fragile lightguide circuit and it can, if desired, also play the role of the bottom portion of the cladding. In addition, it can serve as a fixture to which input and output fibers are attached so as to optically couple cores of an input/output fiber to the cores of the planar lightguide circuit. The fabrication process begins by depositing a base or lower cladding layer of low index silica on the carrier substrate (assuming the substrate itself is not used as the cladding layer). A layer of doped silica with a high refractive index, i.e., the core layer, is then deposited on top of the lower cladding layer. The core layer is subsequently patterned or sculpted into structures required by the optical circuits using photo-lithographic techniques similar to those used in integrated circuit fabrication. Lastly, a top cladding layer is deposited to cover the patterned waveguide core. This technology is well known and is generally described, for example, in U.S. Pat. No. 4,902,086 issued to C. H. Henry et al., and in an article entitled “Glass Waveguides on Silicon for Hybrid Optical Packaging” at pp. 1530–1539 of the Journal of Lightwave Technology, Vol. 7, No. 10, October 1989.
One important passive component that can be fabricated on a PLC is an optical “star coupler” in which waveguides are radially positioned on opposite sides of a slab waveguide. As used in the present invention, a slab waveguide means a planar area, which is large compared to the area of an individual waveguide of the same length, that supports lightwave transmission between input and output waveguides. Optical power entering the slab from input waveguides on one side of the slab is conveyed to output waveguides on the other side. (Ideally, the power is distributed equally among all of the output waveguides.) In an M×N star coupler, for example, the optical power carried by each input waveguide is transmitted across the slab and distributed among the N output waveguides, which are generally arranged in an array. However, if the waveguides in the output array are not well coupled (which is generally the case for star couplers in a so-called “Dragone” router because of the gaps between the array waveguides), then there is a loss of power due to the scattering of light at the junction between the array and the slab. Such losses comprise a major portion of the router's insertion loss.
One technique for reducing the insertion loss of an optical device, such as the aforementioned Dragone router, is taught in a paper entitled “Loss Reduction for Phased-Array Demultiplexers Using a Double Etch Technique,” which was published in Integrated Photonics Research, Technical Digest Series, Vol. 6, Apr. 29–May 2, 1996. In this technique, a transition region having a shallow etch depth is inserted at the junction between the slab and the array waveguides. As might be expected, coupling between adjacent waveguides is improved and coupling losses are decreased. Nevertheless, a greater reduction in insertion loss is desired, and the double etch technique adds a processing step.
Another technique for reducing insertion loss in an optical device is disclosed in U.S. Pat. No. 5,745,618. In this reference insertion loss is reduced between the slab waveguide and the output waveguide array of a star coupler by providing the output waveguide array with a transition region. The transition region includes a number of silica paths that intersect the output waveguide array. One problem with this approach is that it is difficult to manufacture the resulting device because the many small areas adjacent to the intersections between the output waveguides and the silica paths must be completely filled with cladding material, which is difficult to accomplish because of their small dimensions.
Accordingly, it would be desirable to provide an improved technique for reducing insertion loss in an optical device that does not involve additional processing steps and which can be implemented in a highly reliable manner.
In accordance with the present invention, an optical device is provided which includes a slab waveguide and at least one input waveguide coupled to a first side of the slab waveguide. The device also includes a plurality of output waveguides coupled to a second side of the slab waveguide. The slab waveguide has a segmented transition region that includes a plurality of waveguiding regions spaced apart from one other by at least one discrete sector.
In accordance with another aspect of the invention, the plurality of waveguiding regions have widths that progressively decrease as they approach the second side of the slab waveguide.
In accordance with yet another aspect of the invention, the plurality of waveguiding regions and the plurality of output waveguides each comprise a light-carrying core material whose indices of refraction are substantially equal to one another. Additionally, the discrete sectors located between each pair of waveguiding regions may have a lower index of refraction than the waveguiding regions.
In accordance with another aspect of the invention, the discrete sectors have widths that progressively increase as they approach the second side of the slab waveguide. Moreover, the waveguiding regions may be substantially parallel to each other.
In accordance with another aspect of the invention, a planar light-guide circuit is provided. The circuit includes a substrate, a slab waveguide located on the substrate, and at least a first waveguide also located on the substrate and which is coupled to a first side of the slab waveguide. In addition, at least a plurality of second waveguides are located on the substrate and coupled to a second side of the slab waveguide. The circuit also includes N waveguiding regions, where N is an integer greater than or equal to 2. The waveguiding regions are located within the slab waveguide and are spaced apart from one another by segments of predetermined width.
One problem with the known star coupler 201 shown in
The present inventors have recognized that the same advantages which accrue from the star coupler 201 shown in
Returning to
W(330n)+W(340n)=Λ
In the aforementioned embodiment of the invention, the period (Λ)=20 microns. It should be noted that
The use of a transition region in a waveguide slab to reduce insertion loss in accordance with the present invention is applicable to a wide variety of different optical components and is not limited to a star coupler such as shown in
The optical path length of each waveguide in the grating 760 differs from the optical path lengths of all the other waveguides in the grating so that predetermined and different phase shifts are applied to optical signals propagating through the waveguides of the grating from the star coupler 701 because of the different optical path lengths over which the signals in the grating must travel to reach the output of the grating. Accordingly, the optical signals emanating from each of the waveguides of grating 760 have different phases, which are functions of the lengths of the waveguides.
In DWDM 700, demultiplexing is accomplished by transmitting a multiplexed signal through diffraction grating 760, which separates the individual wavelengths of light and diffracts each in a slightly different direction. Multiplexing is accomplished by utilizing DWDM 700 in reverse (i.e., directing each wavelength through the grating at a predetermined wavelength-dependent angle such that all of the wavelengths emerge essentially as one single multiplexed beam of light). The grating function is achieved using an optical, phased array that is constructed from a plurality of waveguides of different lengths. Each waveguide differs in length from its neighboring waveguide by a predetermined amount. The waveguides are substantially uncoupled throughout their entire lengths, except at their ends, where strong mutual coupling between the waveguides is desirable to reduce insertion loss, as explained above. The transition from the coupled portions to the uncoupled portions is gradual, resulting in negligible higher-order mode generation. A discussion of the operation of waveguide grating arrays is presented in U.S. Pat. No. 5,002,350. Moreover, U.S. Pat. No. 5,136,671 is hereby incorporated by reference because it discloses the general design of such DWDMs in greater detail. This type of DWDM structure is also known as a “Dragone” router after its inventor. Significantly, insertion loss is reduced in DWDM 700 by adding transition regions 71 and 72 to waveguide slabs 710 and 720, respectively, whose design is the same as transition region 322 shown in
A 1×N power splitter consists of a single input waveguide that subdivides into a number (N) of output waveguides. Because this structure frequently resembles the branches of a tree, power splitters are often referred to as branch splitters. As shown in
The insertion loss associated with power splitter 801 is decreased by the use of a transition region 82, which is located in slab waveguide 80 and which comprises a number of waveguiding segments 831 . . . 83n. In one embodiment of the invention slab waveguide 80 has a length of about 500 microns and over this length its width gradually increases from about 7 microns to about 100 microns. The waveguiding segments 831 . . . 83n comprising transition region 82 are generally parallel to each other and have widths that progressively decrease as they become closer to the output waveguides 86. The construction of transition region 82 is substantially the same as the construction of transition region 322, which was discussed in connection with
Although various particular embodiments of the present invention have been shown and described, modifications are possible within the spirit and scope of the invention. These modifications include, but are not limited to: use of the inventive transition region on the input side of the slab waveguide instead of the output side, or on multiple sides of a slab waveguide; decreasing the widths of the waveguiding segments that comprise the transition region in a non-linear manner; and using the inventive transition region on less than all of the waveguides in an array.
Patent | Priority | Assignee | Title |
10054738, | May 27 2010 | NTT Electronics Corporation | Optical waveguide and arrayed waveguide grating |
10330863, | Apr 18 2017 | NeoPhotonics Corporation | Planar lightwave circuit optical splitter / mixer |
10859769, | Sep 06 2018 | Mitsubishi Electric Research Laboratories, Inc. | Compact photonic devices |
11061187, | Apr 18 2017 | NeoPhotonics Corporation | Planar lightwave circuit optical splitter/mixer |
7130518, | Dec 19 2003 | NEC Corporation | Optical coupler, beam splitter, and arrayed waveguide grating type optical wavelength division multiplexer |
7212709, | Jul 02 2004 | NEC Corporation | Optical waveguide device and optical waveguide module |
7343071, | Jun 04 2002 | Ignis Photonyx AS | Optical component and a method of fabricating an optical component |
8126300, | Jun 17 2008 | Enablence Inc. | Segmented waveguide structure |
9020310, | Nov 09 2010 | NTT Electronics Corporation | Optical waveguide and arrayed waveguide grating |
9075191, | Dec 22 2010 | NTT Electronics Corporation | Optical waveguide and arrayed waveguide grating |
9618694, | May 27 2010 | NTT Electronics Corporation | Optical waveguide and arrayed waveguide grating |
Patent | Priority | Assignee | Title |
4902086, | Mar 03 1988 | AT&T Bell Laboratories | Device including a substrate-supported optical waveguide, and method of manufacture |
5002350, | Feb 26 1990 | AT&T Bell Laboratories | Optical multiplexer/demultiplexer |
5136671, | Aug 21 1991 | AT&T Bell Laboratories; AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NY | Optical switch, multiplexer, and demultiplexer |
5745618, | Feb 04 1997 | THE CHASE MANHATTAN BANK, AS COLLATERAL AGENT | Optical device having low insertion loss |
20020131704, | |||
20020159696, | |||
20020172460, | |||
20030012497, |
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